1. Field of the Invention
The present invention relates generally to antimony oxide-containing glass compositions and, more particularly, to optically active antimony oxide-containing glasses that are made optically active by being doped with a rare earth element; their use in optical amplifying devices and optical amplifying devices incorporating these compositions; and methods for making the glass compositions of the invention. As used herein, the term xe2x80x9coptically activexe2x80x9d refers to a rare earth doped glass capable of stimulated emission for amplifying a light signal when the glass is excited by a suitable pumping source.
2. Technical Background
It is known that single mode optical fibers doped with low levels of rare-earth ions can be drawn from heavy metal fluoride glasses. Unfortunately, heavy metal fluoride glasses suffer certain undesirable attributes that have restricted their applications. Most notably, heavy metal fluoride glasses exhibit poor resistance to devitrification. U.S. Pat. No. 4,674,835 discusses the crystallization problems of heavy metal fluoride glasses, one example of which is referred to as ZBLAN, and the light scattering problems resulting therefrom. The susceptibility of heavy metal fluoride glasses to devitrification generates problems in making large preforms. Crystallization in the preform causes difficulties during the formation of optical fibers by commonly used methods. Heavy metal fluoride glasses are quite prone to inhomogeneous nucleation, which leads to crystallization at the core and cladding interfaces during the drawing of the optical fiber. The resulting crystals in the fibers cause serious light scattering losses.
Devitrification of the heavy metal fluoride glasses is aggravated when ions necessary to impart differences in indices of refraction to the core and cladding are added to the glass composition. Additional doping, for example, with rare earth metal ions, also tends to reduce the stability of the glass. As a consequence of those problems, research has focused on finding additives to a base fluoride glass composition that will reduce the tendency of the glass to devitrify and to increase the chemical stability thereof. However, the preparation of fluoride glasses requires that the glass forming components be reheated at high temperatures. Furthermore, these glasses cannot be melted in air but require a water-free, inert gas environment.
Most oxide glasses such as, for example, silicon dioxide, are easier to prepare, more chemically and mechanically stable, and more easily fabricated into rods, optical fibers, or planar waveguides than are fluoride glasses. Addition of even small amounts of oxides into fluoride glasses to improve their stability significantly quenches their upconversion luminescence.
Rare earth-doped glasses have found frequent use for the fabrication of light-generating and light-amplifying devices. For example, U.S. Pat. No. 3,729,690 describes a laserable glass comprising a host material that contains a fluorescent trivalent neodymium ingredient. U.S. Pat. No. 5,027,079 discloses an optical amplifier comprising a single mode fiber that has an erbium-doped core. U.S. Pat. No. 5,239,602 discloses an apparatus and method for flattening the gain of an optical amplifier that utilizes an erbium-doped silica fiber having a germanosilicate core. U.S. Pat. No. 5,563,979 discloses an erbium-doped planar optical device whose active core includes a mixture of oxides such as lanthanum and aluminum oxides. The inclusion of antimony oxide in glasses for optical devices is also reported. One reference describes a glass for use in waveguides that contains 50-75 mole % Sb2O3.
For the construction of efficient optical amplifiers, there remains a need for new, readily prepared glasses that display an optimal combination of gain flatness and breadth. This need is well met by the glass of the present invention.
According to one aspect of the present invention an optically active glass contains Sb2O3, up to about 4 mole % of an oxide of a rare earth element, and 0-20 mole % of a metal halide selected from the group consisting of a metal fluoride, a metal bromide, a metal chloride, and mixtures thereof, wherein this metal is a trivalent metal, a divalent metal, a monovalent metal, and mixtures thereof. In addition, any of the glass compositions described herein may contain up to 10 mole % B2O3 substituted for an equivalent amount of Sb2O3.
Although the glass of the present invention is highly desirable because it can be fabricated in air using standard melting techniques and batch reagents, when the glass contains about 90% or more of Sb2O3 it is formed by the techniques of splat quenching or roller quenching. The glass composition of the present invention exhibits a gain spectrum with excellent breadth and flatness characteristics and can be readily modified for specific optical amplifier applications.
Further in accordance with the present invention is an optical energy producing or light-amplifying device, in particular an optical amplifier or laser, that comprises the glass of the invention. The optical amplifier can be either a fiber amplifier or a planar amplifier, either of which may be of a hybrid (composition) construction.